1. Field of the Invention
The present invention relates to an apparatus for optically reproducing data from, e.g., a card- or disk-like optical data recording medium.
2. Description of the Related Art
An optical card is known as an example of such a recording medium. An example of the optical card is described in Published Unexamined Japanese Patent Application No. 63-37876 filed by the assignee of the present invention. FIG. 1 shows this optical card.
An optical recording portion 4 comprising a plurality of parallel tracks 4a is formed on the upper surface of an optical card 2 having a shape similar to that of a credit card or the like. Data can be recorded by forming data pits in the tracks 4a, or be reproduced by reading the data pits formed in the tracks 4a. Data is written or read by scanning a light beam emitted from an optical head (not shown) onto the tracks 4a. Scanning is normally performed by repeatedly moving the optical card 2 in the direction of tracks. Therefore, the scanning directions are sometimes opposite between write and read operations. In this case, the readout data train of one track is inverted in the direction of time axis by using a buffer memory, so that data can be correctly read.
ID portions 6a and 6b are formed on the two end portions of each track 4a to record data (ID data) indicating a track address corresponding to this track 4a. The end portions of the tracks 4a have a low reliability since they can be easily damaged or soiled. Therefore, the ID portions 6a and 6b are formed at positions inward from the card ends at predetermined distances (e.g., 4 mm). This also aims at sufficiently stabilizing the relative moving speed of the optical card 2 and the optical head (light beam). A portion between the two ID portions 6a and 6b forms a data portion 8 for recording data. As described above, scanning is performed by reciprocal conveyance of the card, and data is reproduced in the two directions. Hence, the ID portions 6a and 6b are formed on the two sides of the data portion 8 so that the track address can be read from either side. For this purpose, when the light beam is moving from, e.g., the left to the right in FIG. 1, the ID portion 6a on the left side is read; when the light beam is moving from the right to the left, the ID portion 6b on the right side is read, thereby recognizing the track address. In this manner, the ID data can be read regardless of the scanning direction before the data portion 8 is read.
The conventional optical card data reproducing apparatus described above is of a single track read type which reads data in units of tracks by radiating a light beam emitted from the optical head onto only a single track.
However, in such a single track read type apparatus, the reproducing speed of data recorded on the track is determined by the relative speed of the optical head and the recording medium and cannot be freely increased.
In order to solve this drawback, a simultaneous read type reproducing apparatus for simultaneously reading a plurality of tracks is proposed. According to this apparatus, a beam emitted from an optical head is radiated on a plurality of tracks, thereby reading data from the plurality of tracks simultaneously.
For example, U.S. Pat. application No. 904,036 (filed Jun. 25, 1992) filed by the same assignee as that of the present invention discloses such a multi-track read type apparatus. In this apparatus, data reproducing means each comprising a data reproducing photodetector, a binarization circuit, a bit clock generator, a demodulator, and a buffer memory are provided in a number corresponding to the number of a plurality of tracks that are to be read simultaneously. Therefore, when data is to be read from the optical card, processing of binarization, demodulation, and memory storage is executed for the plurality of tracks simultaneously in a parallel manner. After the optical head passes the data portion 8, the errors of the demodulated data stored in the memory are sequentially corrected by an error correcting means. Then, even when the relative speed of the optical head and the recording medium is high, the data read speed can be increased. A simultaneous read type apparatus of this type for reading a plurality of tracks simultaneously can also be used as a single track read type apparatus.
Generally, in the optical card 2 shown in FIG. 1, each of the ID portions 6a and 6b includes, i.e., five items of ID data ID0 to ID4. The ID data ID0 to ID4 include the same track address data and are usually subjected to error correction encoding.
In the data recording/reproducing apparatus for an optical card, for example, when a read access request from a host computer to which this apparatus is connected designates a track address, a track at an estimated position is scanned to read its address. If this address coincides with the address of the target track, the readout data is fetched. If this address does not coincide with the address of the target track, this scanning is nullified, and the target track is read in the subsequent scanning operation. This procedure also applies to the data write operation.
In this data recording/reproducing apparatus, erroneous track address recognition leads to damaging already recorded data or reading erroneous data. Therefore, a probability of erroneous track address recognition must be minimized as much as possible. For this purpose, five items of ID data ID0 to ID4 are recorded on each of the ID portions 6a and 6b. The track address is determined based on the read result of the five items of ID data ID0 to ID4, thereby suppressing the probability of erroneous recognition.
In the data reproducing apparatus using this optical card 2, recording/reproduction of data is generally performed by reciprocally moving the optical card and the optical head in the direction of tracks relative to each other. The moving speed (i.e., the relative speed of the optical head and the optical card in the scanning operation of the light beam) in the reciprocal movement will be briefly described with reference to FIG. 3.
Assume that the optical head is located on the left side of the ID portion 6a of FIG. 1. One scanning operation is started at time 0, and the scanning speed is increased so that the relative speed (scanning speed) of the optical head and the optical card becomes a predetermined constant speed before the optical head reaches the start position of the left ID portion 6a (time t1).
When the optical head reaches the ID portion 6a, the scanning speed becomes the constant speed, the ID portion 6a is read, and thus the track address is confirmed. Thereafter, scanning of the data portion 8 is started and the optical head accesses the data portion 8. When the optical head passes by the right ID portion 6b (time t2), the scanning speed is started to be decreased so as to stop the scanning operation. When a predetermined setting time has lapsed after time t3 at which the reciprocal movement of the optical head and card is stopped, the subsequent scanning operation in the opposite direction is started at time t4.
In this manner, the optical head and card are reciprocally moved relative to each other in the direction of tracks to move the light beam to be radiated on the optical card along the track, thereby recording/reproducing data.
As described above, in the conventional optical card recording/reproducing apparatus, an ID portion (the ID portion 6a in the case of FIG. 3) appearing immediately before accessing the data portion 8 is read, as shown in FIG. 3. The track address of the track which is being scanned is identified from the content of this ID portion. It is recognized that a data portion following this ID portion is the area corresponding to a desired track address. Then, data recording/reproduction is performed.
At this time, all the contents of the plurality of items of ID data ID0 to ID4 that are read when the ID portion 6a or 6b is scanned are subjected to error correction encoding to reproduce the corresponding track address data (track number). If the same track address data can be reproduced from all items of the ID data, the data portion 8 is reproduced. If the same track address data cannot be reproduced, the data portion 8 is not reproduced.
More specifically, in the conventional apparatus, when the ID portion 6a or 6b cannot be read at all due to dust or scratches, or when even at least one ID data, of the five items of ID data written on the ID portion, cannot be read correctly, it is determined that the probability of erroneous track address recognition is high, and the data portion is not reproduced.
Even in this case, however, regarding the relative scanning operation of the optical card and head, a normal scanning operation similar to that shown in FIG. 3 is executed so that the next scanning operation is performed from the opposite side. In the next scanning operation from the opposite side, the ID portion 6b is read from the right side of the optical card 2 shown in FIG. 1. The track address is recognized from the content of the ID portion 6b. If the track address is normally recognized, the data portion is reproduced.
Thus, in conventional data reproduction from an optical card, while the normal reciprocal scanning operation of the tracks is repeated, the track address is identified from an ID portion appearing before reading the data portion. If a track address can be identified, the following data portion is read. If the track address cannot be identified, or when it is determined that the probability of erroneous recognition is high, the readout data is not fetched, and this one scanning operation is nullified.
This wasteful scanning prevents the improvement of data read efficiency. Considering that the optical card is a medium capable of handling a great deal of data, it is an important problem to improve an efficiency of reading data.
Furthermore, even when the track address is identified, if this track address is different from that of a target track which is requested to be accessed, this scanning operation is nullified at all, and readout data obtained by this scanning is not utilized.